If you're not as relaxed as your partner, you benefit the relationship in other ways.

RODALE NEWS, EMMAUS, PA—You would likely agree that it’s better to feel happy and secure about yourself and your relationships than the alternative. People who are like this have what psychologists call a “secure attachment style” toward others. They’re optimists, and they usually function well in groups. Yet, rather oddly, around half the human population falls in the opposite camp, say Israeli researchers. These people tend to be less happy, somewhat pessimistic, have more difficulty in relationships, and exhibit an “insecure attachment style” with others.

Which begs the question: Why has half the human population evolved to the point where they remain essentially insecure? Part of the reason, according to the Israeli study, is because insecure people bring some critical things to the table. Among them: alertness to dangers, along with a propensity to take quick action. More secure people seem not to be as accomplished at either. Or course, people shouldn't spend their days being miserable in a relationship they have no faith in. But it's possible that a little insecurity in relationships may be accompanied with some positive side effects.

THE DETAILS: In a new review of research on the topic, coauthor Tsachi Ein-Dor and colleagues in the New School of Psychology at the Interdisciplinary Center in Herzliya, Israel, revisit attachment theory, an idea first proposed in the 1950s. Based on early influences like the attachments we make to our parents and caregivers, some people form secure attachment styles, while others form insecure attachment styles, according to the theory. The good news, this new research suggests, is that even if your style isn't as secure is it could be, you may bring other things to the table. Ein-Dor believes that both styles are important to the success of human society.

WHAT IT MEANS: If you tend to have trouble with relationships, you're probably better at spotting other kinds of trouble. “For example, secure people, because of their sense of security, tend to overlook initial signs of danger,” says Ein-Dor. “These might be sirens, sounds, and—on a more personal level—clues of infidelity by a spouse." These people also tend to delay in taking action, because they work better in groups, and group-level action takes longer. But anxiously attached people tend to be more vigilant than secure. "They won’t overlook initial signs of danger, will take them seriously, and will alert others or take action themselves. In this way, insecure people act as sentinels,” Ein-Dor says.